Well-treated hypertensive but otherwise healthy people had an abnormal circadian blood pressure variation, although their average 24-hour ambulatory blood pressure was well controlled compared with healthy controls. Brain glucose metabolism was decreased in several brain areas in hypertensive subjects without end-organ damage, particularly in territories of the perforating arteries, but coupling between flow and metabolism was preserved. Patients with sleep apnea syndrome, a model for reversible vascular dementia, scored worse than controls on tests of attention, visuoperceptual and -spatial functions, and had reduced metabolism in the right amygdala, left hippocampus, and left medial parietal cortex, possibly accounting for the cognitive deficits. White matter hyperintensities (on magnetic resonance imaging), often found in vascular dementia, are predictive of metabolic brain alterations and cognitive deficits even in healthy subjects. Patients with Alzheimer's disease (AD) who had white matter changes showed reduced metabolism in subcortical gray matter and calcarine cortex compared with AD patients without white matter changes, suggesting that leukoencephalopathy influences metabolic abnormalities in AD. On postmortem, white matter changes were related to amyloid angiopathy.